1. Field of the Invention
This invention relates to metal articles made from dissimilar metals. It also relates to improved methods of making saw blades, and in particular, composite saw blades.
2. Description of Related Art
Saw bands and saw blades must have high dimensional stability of their cutting edges as well as high wear resistance. They should also be able to withstand the high loading produced by compressive, flexural and shearing forces, even under the temperatures that result from the friction between the saw blade and the material being sawn. Since it is difficult to combine the properties mentioned above in a single material, saw blade nowadays usually comprise a relatively tough metal base with high bending fatigue strength and a cutting-edge band of a high-speed steel that is less tough but highly wear resistant. The cutting-edge band is of such a width that at least the teeth tips of the saw band or blade, or even the cutting teeth as a whole, can be cut out from it.
Composite saw blades, that is, saw blades made up of two or more dissimilar materials, have been prepared by welding a thin strip of cutting tool steel to an edge of a flexible alloy steel backer. A common welding technique is electron beam welding; however, the resulting weld, an alloy of the two metals and a heat-affected area adjacent to it, is materially weakened. In preparation for welding, and in particular for electron beam welding, the metal backer and the thin strip of cutting tool steel are rolled and annealed repeatedly to attain the desired dimensions for welding. When welding dimensions are achieved, both the metal backer and the strip still needs to be further conditioned to obtain sharp, square edges at the site of welding. This process can be very time consuming and costly.
Composite metal articles also have been prepared by casting molten cutting tool steel against a supporting metal strip. The molten cutting tool steel is fed into a space adjacent to the supporting metal strip, where it bonds.
Solid phase edge bonding has been used for side-by-side joining of metal strips by application of heat and pressure under a reducing atmosphere. Solid phase bonding is accomplished by heating the metal strips under sufficient pressure to form a metallurgical bond. Although solid state bonding can produce a metallurgical bond without deleterious effect to neighboring metal area, solid state edge bonding does not generate sufficient new bonding surfaces, heat and pressure to form a strong bond, and the joined strips often do not survive subsequent processing.
Hot rolling of metals is known, and the hot rolling of steel ingots has been in common practice for many years. Hot rolling is usually carried out at temperatures around 2000° F., and the hot rolled steel typically is cold-rolled to its final dimensions. It is often necessary when rolling high speed steel to anneal the steel after each 10% to 30% cold worked reduction due to damage, i.e., work hardening, resulting from cold working. Thus, cold working requires additional time-consuming and costly processing steps.
Hot bonding has been used to prepare composite metal articles such as copper clad steel by heating a steel core and two copper strips to hot rolling temperatures using electric resistance heating. The three components are introduced into a chamber with a reducing atmosphere and are then passed directly into a roll, where pressure and heat bond the materials. As with hot rolling, it is most often necessary to cold work the article to its final dimensions.
Thus, improved methods for providing composite articles having high bond strength between different metals are desired.
There remains a need for efficient manufacture of composite metal articles.
There remains a further need for composite metal articles having a strong bond between the component metals with minimal material damage to the bonding region.
These and other limitations of the prior art are addressed in the following invention.